Reading spectacles

Abstract

Reading spectacles are tested for acceptability by a user by providing each lens with a releasable opaque film having a small circular window aligned with the optical centre of the lens. Acceptable spectacles are determined by the optical centers of the lenses being sufficiently aligned with the optical centers of the eyes to permit reading through the restricted field of view afforded by the windows.

I claim: 
     
       1. A method of preparing a pair of reading spectacles for testing by a user, wherein a mask is applied to each lens of the spectacles, the mask having therein a window whose centre corresponds substantially to the optical centre of the lens, the size of the window being determined in accordance with an inverse relationship to the strength of the lens. 
     
     
       2. A method as claimed in claim 1, wherein the radial extent of the window from the optical centre of the lens is of the same order as the maximum permitted deviation of the optical centre of the lens from the optical centre of the eye of a user, for the lens strength concerned. 
     
     
       3. A method as claimed in claim 1 or claim 2, wherein the lens strengths are in the range of +0.50 up to +3.50 diopters and the windows have a corresponding radial extent in the range of 5 mm down to 0.5 mm in accordance with the lens strength. 
     
     
       4. A method of preparing and testing a pair of reading spectacles by a user for correspondence of the optical centres of the spectacle lenses to the optical centres of the eyes, comprising the steps of: (a) providing a mask having a window for each lens of the spectacles wherein the size of the window is determined in accordance with an inverse relationship to the strength of the lens;   (b) applying each mask to each lens of the spectacles so that the centre of each window corresponds substantially to the optical centre of the lens; and   (c) wearing the spectacles and looking through the windows to determine if the optical centres of the lenses are sufficiently aligned with the optical centres of the eyes.   
     
     
       5. The method of claim 4 wherein the radial extent of each window from the optical centre of the lens is of the same order as the maximum permitted deviation of the optical centre of the lens from the optical centre of the eye of the user for a given lens strength. 
     
     
       6. The method of claim 4 or claim 5 wherein the lens strengths are in the range of +0.50 up to +3.50 diopters and the windows have a corresponding radial extent in the range of 5 mm down to 0.5 mm in accordance with the lens strength. 
     
     
       7. The method of claim 4 further including the step of repeating steps (a) through (c) with plural spectacles having different lens strengths.